Absolutely correct, I think. CAA have the international legal obligation to monitor 121.5, which they gave to NATS. NATS supplied the military with the kit to monitor 121.5 because they were already looking after 243.0. Who pays for that element of the service provision? Sorry, you'd have to ask someone a lot cleverer than I.
As to who would have to pay for the kit? Don't know. It wouldn't be NATS as they're not obligated to provide a practise VHF. We provide a practise UHF (245.1) for flt safety reasons. We wouldn't provide funding for a practise VHF because we're already doing NATS a favour looking after 121.5-although this works in our favour in a number of ways that have already been mentioned. Central government through the DoT?